A conventional automatic transmission is ordinarily configured so that by a driver sliding a sliding shift lever provided at the driver's seat, the force of that sliding operation is directly transmitted to a parking mechanism or a manual valve by a wire, a rod, or the like, and thus the driver selects, for example, any of a parking range P, a reverse (rearward travel) range R, a neutral range N, and a drive (forward travel) range D.
Here, when the parking range P has been selected, the parking mechanism establishes a locked state in which it is not possible to rotate an output shaft of the automatic transmission. When the reverse range R, the neutral range N, or the drive range D has been selected, the requested range is established by engaging or releasing a frictionally engaged element such as a clutch or a brake provided in a transmission mechanism unit by changing the state of a manual valve that is one constituent element of a shift range switching hydraulic circuit provided in the automatic transmission.
Next is a description of the configuration and operation of the above parking mechanism.
The parking mechanism is ordinarily configured to include a parking gear, a parking lock pole, and a parking rod.
The parking gear is externally fixed to the output shaft of the automatic transmission. The parking lock pole is supported so as to be capable of tilting to be displaced towards or away from the parking gear, and has a catch that can be engaged between teeth of the parking gear, or disengaged. A tapered cone for tilting the parking lock pole is provided at one end of the parking rod, and the parking rod is displaced frontward or rearward approximately parallel to the output shaft of the automatic transmission. This parking rod is driven by a detent lever that drives the manual valve.
As for operation of the parking mechanism, first, when the parking rod is, for example, displaced rearward by tilting the detent lever, the tapered cone pushes up the parking lock pole, so that the catch of the parking lock pole engages between the teeth of the parking gear, and thus the locked state in which it is not possible to rotate the output shaft of the automatic transmission is established.
On the other hand, when the parking rod is, for example, displaced frontward by tilting the detent lever in the opposite direction as described above, force of the tapered cone pushing up the parking lock pole is released, and the parking lock pole is pulled with a spring and thus moves downward, so the catch of the parking lock pole is pulled out from between the teeth of the parking gear, and thus the unlocked state in which it is possible to rotate the output shaft of the automatic transmission is established.
Incidentally, as the mode of operation of the detent lever, there is a so-called direct operation method in which the shift lever is directly linked in communication with the detent lever by, for example, a wire, a rod, or the like, and the detent lever is directly driven by operating force of the shift lever, and there is also a so-called shift-by-wire method.
In the shift-by-wire method, operation of the shift lever by the driver is detected with a sensor, a switch, or the like, and the detent lever is operated by an appropriate actuator according to the detected shift range signal (for example, see Patent Documents 1 and 2).
In the case of a shift-by-wire method, other than the above ordinary shift lever, a joystick, a push-button, or the like may be used as an operation member that outputs a parking request signal or a parking release request signal of the parking mechanism.
Further, when providing a shift-by-wire parking mechanism, it is known to perform so-called auto parking control in which, without operating the operation member, the parking mechanism is set to the locked state by driving the actuator when, for example, a predetermined condition has been established (e.g., see Patent Document 3).    Patent Document 1: JP H5-280637A    Patent Document 2: JP 2005-69407A    Patent Document 3: JP H6-72296A